The present disclosure relates to a light source apparatus, an image display apparatus, and an optical unit.
Recently, products including solid-state light sources such as a light-emitting diode (LED) and a laser diode (LD) have been increasingly used. The solid-state light sources are adopted as light sources used in projectors for presentation and digital cinema, instead of mercury lamps, xenon lamps, and the like used in related art. The fixed light sources such as LEDs have advantages such as having long lifetime, omitting the replacement of lamps, which is necessary in related art, and lighting-up immediately after power-on.
For example, Japanese Patent Application Laid-open No. 2012-173593 discloses a projector in which a solid-state light source is used as an excitation light source. Blue laser light output from the solid-state light source is applied to a phosphor wheel as excitation light. The phosphor wheel includes a base and a phosphor layer formed thereon. When the excitation light is applied to the phosphor layer, a yellow phosphor is emitted. The blue light and yellow light emitted from the phosphor layer are combined, and thus white light is emitted (Japanese Patent Application Laid-open No. 2012-173593, paragraphs [0028] and [0029], etc.).
In the projector disclosed in Japanese Patent Application Laid-open No. 2012-173593, in order to improve cooling performance of the phosphor wheel that generates heat by the application of the laser light, a crystalline member such as crystal and sapphire excellent in thermal conductivity is used for the base of the phosphor wheel. However, since this type of crystalline material has a crystal axis, when a phosphor wheel made of such a crystalline material is rotated, a relationship between the polarization direction of the laser light and the crystal axis direction of the crystalline member constantly changes. This leads to disturbances of the polarization direction of the laser light (Japanese Patent Application Laid-open No. 2012-173593, paragraphs [0005] and [0006], etc.). To eliminates such a disadvantage, in Japanese Patent Application Laid-open No. 2012-173593, the thickness of the crystalline member is defined within a predetermined range based on a complex index of refraction of the crystalline member or a wavelength of light output from a light source (Japanese Patent Application Laid-open No. 2012-173593, paragraphs [0009] and [0013], etc.).